Targeted Radiolabeled Compounds in Glioma Therapy

A multivariate retrospective analysis of high-grade gliomas: Survival and prognostic factors

OBJECTIVES

High-grade gliomas (HGGs) are highly malignant, aggressive, and have a high incidence and mortality rate. The aim of this study was to investigate survival outcomes and prognostic factors in patients with HGGs.

METHODS

In this retrospective study, a total of 159 patients with histologically confirmed HGGs were included. The recruitment period was from January 2011 to December 2019. We evaluated patient demographic data, tumor characteristics, treatment methods, immunocytochemistry results, overall survival (OS) time, and progression-free survival (PFS) time using Kaplan-<>Meier survival analysis with log-rank testing. Additionally, we employed Cox regression analysis to identify independent factors associated with survival outcomes.

RESULTS

Kaplan-Meier survival analysis revealed that the 1-, 2-, and 5-years OS rates were 81.8%, 50.3%, and 12.6%, respectively. Similarly, the 1-, 2-, and 5-years PFS rates were 50.9%, 22.4%, and 3.1%, respectively. The median OS duration was 35.0 months. The univariate analysis indicated that postoperative pathological classification, grade, and age were significantly associated with patient outcomes (p < 0.01). Among the patients, 147 received concurrent chemoradiotherapy, while 12 did not. The immunohistochemical markers of ki-67, MGMT, IDH1R132H, and p53 demonstrated statistically significant differences in their prognostic impact (p = 0.001, p = 0.020, p = 0.003, and p = 0.021, respectively). In conclusion, we found that grades, age, pathological classification, ki-67, MGMT, and IDH1R132H expression were statistically significantly associated with PFS (p < 0.01, p = 0.004, p = 0.003, p = 0.001, p = 0.036, and p = 0.028). Additionally, immunohistochemical expressions of TRIB3 and AURKA were significantly higher in patients with shorter survival (p = 0.015 and p = 0.023).

CONCLUSIONS

Tumor grade and the use of concurrent chemoradiotherapy after surgery were independent prognostic factors that significantly influenced patient survival. Additionally, tumor grade and MGMT expression were found to be independent factors affecting progression-free survival (PFS). Notably, the expression of TRIB3 and AURKA was higher in patients with poor survival outcomes.

Exploring the causal relationship between antihypertensive drugs and glioblastoma by combining drug target Mendelian randomization study, eQTL colocalization, and single-cell RNA sequencing

Recent reports indicate a potential oncogenic role of antihypertensive drugs in common cancers. However, it remains uncertain whether this phenomenon influences the risk of glioblastoma multiforme (GBM). This study aimed to assess the potential causal effects of blood pressure (BP) and antihypertensive drugs on GBM. Genome-wide association study (GWAS) summary statistics for systolic blood pressure (SBP), diastolic blood pressure (DBP), and GBM in Europeans were downloaded. To represent the effects of antihypertensive drugs, we utilized single nucleotide polymorphisms (SNPs) associated with SBP/DBP adjacent to the coding regions of different antihypertensive drugs as instrumental variables to model five antihypertensive drugs, including angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers, β-receptor blockers (BBs), and thiazide diuretics. Positive control studies were performed using GWAS data in chronic heart failure. The primary method for causality estimation was the inverse-variance-weighted method. Mendelian randomization analysis showed that BBs with the β1-adrenergic receptor (ADRB1) as a therapeutic target could significantly reduce the risk of GBM by mediating DBP (OR = 0.431, 95% CI: 0.267-0.697, p < .001) and that they could also significantly reduce the risk of GBM by mediating SBP (OR = 0.595, 95% CI: 0.422-0.837, p = .003). Sensitivity analysis and colocalization analysis reinforced the robustness of these findings. Finally, the low expression of the ADRB1 gene in malignant gliomas was found by GBM data from TCGA and single-cell RNA sequencing, which most likely contributed to the poor prognosis of GBM patients. In summary, our study provides preliminary evidence of some causal relationship between ADRB1-targeted BBs and glioblastoma development. However, more studies are needed to validate these findings and further reveal the complex relationship between BP and GBM.

Targeted Glioma Therapy-Clinical Trials and Future Directions

Glioblastoma multiforme (GBM) is the most common type of glioma, with a median survival of 14.6 months post-diagnosis. Understanding the molecular profile of such tumors allowed the development of specific targeted therapies toward GBM, with a major role attributed to tyrosine kinase receptor inhibitors and immune checkpoint inhibitors. Targeted therapeutics are drugs that work by specific binding to GBM-specific or overexpressed markers on the tumor cellular surface and therefore contain a recognition moiety linked to a cytotoxic agent, which produces an antiproliferative effect. In this review, we have summarized the available information on the targeted therapeutics used in clinical trials of GBM and summarized current obstacles and advances in targeted therapy concerning specific targets present in GBM tumor cells, outlined efficacy endpoints for major classes of investigational drugs, and discussed promising strategies towards an increase in drug efficacy in GBM.

Peptides for trans-blood-brain barrier delivery

Trans-blood-brain barrier (BBB) delivery of therapeutic and diagnostic agents is a major challenge in the development of central nervous system (CNS) targeted radiopharmaceuticals. This review is an introduction to the use of peptides as delivery agents to transport cargos into the CNS. The most widely used BBB-penetrating peptides are reviewed here, with a particular emphasis on the broad range of cargos delivered into the CNS using these. Cell-penetrating peptides (CPPs) have been deployed as trans-BBB delivery agents for some time; new developments in the CPP field offer exciting opportunities for the design of next generation trans-BBB complexes. Many of the peptides highlighted here are ready to be combined with diagnostic and therapeutic radiopharmaceuticals to develop highly effective CNS-targeted agents.

Clinical Advances and Perspectives in Targeted Radionuclide Therapy

Targeted radionuclide therapy has become increasingly prominent as a nuclear medicine subspecialty. For many decades, treatment with radionuclides has been mainly restricted to the use of iodine-131 in thyroid disorders. Currently, radiopharmaceuticals, consisting of a radionuclide coupled to a vector that binds to a desired biological target with high specificity, are being developed. The objective is to be as selective as possible at the tumor level, while limiting the dose received at the healthy tissue level. In recent years, a better understanding of molecular mechanisms of cancer, as well as the appearance of innovative targeting agents (antibodies, peptides, and small molecules) and the availability of new radioisotopes, have enabled considerable advances in the field of vectorized internal radiotherapy with a better therapeutic efficacy, radiation safety and personalized treatments. For instance, targeting the tumor microenvironment, instead of the cancer cells, now appears particularly attractive. Several radiopharmaceuticals for therapeutic targeting have shown clinical value in several types of tumors and have been or will soon be approved and authorized for clinical use. Following their clinical and commercial success, research in that domain is particularly growing, with the clinical pipeline appearing as a promising target. This review aims to provide an overview of current research on targeting radionuclide therapy.

CircNDC80 promotes glioblastoma multiforme tumorigenesis via the miR-139-5p/ECE1 pathway

BACKGROUND

Circular RNAs (circRNAs) have been shown to be essential for the emergence and growth of different cancers. However, further research is required to validate the function of circRNA in glioblastoma (GBM).

METHODS

CircNDC80 expression in both normal brain tissues (NBTs) and glioma tissues was determined using real-time PCR. The impact of circNDC80 on GBM cell proliferation, migration, and invasion was then confirmed by CCK-8, colony formation, EdU incorporation, Transwell, and wound healing assays. To determine how circNDC80 affects the capacity of glioma stem cells (GSCs) to maintain their stemness and self-renewal, a CellTiter-Glo assay, clonogenic assay and extreme limiting dilution assay were utilized. To ascertain the impact of circNDC80 in vivo, intracranial xenograft models were established.

RESULTS

When compared to NBT, glioblastoma tissue had a higher level of circNDC80 expression. In functional assays, circNDC80 promoted glioblastoma cell proliferation, migration, and invasion, while sustaining the stemness and fostering the self-renewal of glioma stem cells. In addition, a dual luciferase reporter assay and circRIP were used to verify that circNDC80 simultaneously affects the expression of ECE1 mRNA by sponging miR-139-5p, and a rescue experiment was used to verify the above results further.

CONCLUSIONS

According to our research, circNDC80 is an oncogenic factor that promotes glioblastoma through the miR-139-5p/ECE1 pathway. This implies that circNDC80 may be employed as a novel therapeutic target and a possible predictive biomarker.

Identification of the miR-423-3p/VLDLR Regulatory Network for Glioma Using Transcriptome Analysis

As the most prevalent primary CNS tumor, glioma is characterized by high mortality and morbidity. This research aims to investigate glioma-associated microRNAs (miRNAs) and their target mRNAs, as well as to explore their biological functions in gliomas. The Gene Expression Omnibus (GEO) database was applied to acquire the GSE112264 miRNA microarray dataset and the GSE15824 mRNA dataset. We selected samples from the GSE112264 dataset and the GSE15824 to identify differently expressed miRNAs (DE-miRNAs) as well as differentially expressed mRNAs (DEGs), respectively. Next, the intersections of mRNA and target mRNAs of miRNA were selected, and we constructed miRNA-mRNA regulation networks. These DEGs were selected for Gene Oncology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses by conducting the package clusterProfiler. After conducting Cytoscape software, a protein-protein interaction (PPI) network was created. Next, survival analysis of the miR-423-3p was confirmed by conducting TCGA database. Subsequently, Quantitative real-time PCR (qRT-PCR) was conducted to verify miR-423-3p's expression. Finally, miR-423-3p's biological functions of in effecting the cell proliferative, migratory, and invasive capabilities of glioma were investigated by performing Cell Counting Kit-8 (CCK-8) and Transwell assays. Our analysis elucidated a novel miRNA-mRNA regulatory network related to glioma carcinogenesis, which may be considered as future therapeutic biomarkers for glioma.

Diffusing alpha-emitters radiation therapy in combination with temozolomide or bevacizumab in human glioblastoma multiforme xenografts

Glioblastoma multiforme (GBM) is at present an incurable disease with a 5-year survival rate of 5.5%, despite improvements in treatment modalities such as surgery, radiation therapy, chemotherapy [e.g., temozolomide (TMZ)], and targeted therapy [e.g., the antiangiogenic agent bevacizumab (BEV)]. Diffusing alpha-emitters radiation therapy (DaRT) is a new modality that employs radium-224-loaded seeds that disperse alpha-emitting atoms inside the tumor. This treatment was shown to be effective in mice bearing human-derived GBM tumors. Here, the effect of DaRT in combination with standard-of-care therapies such as TMZ or BEV was investigated. In a viability assay, the combination of alpha radiation with TMZ doubled the cytotoxic effect of each of the treatments alone in U87 cultured cells. A colony formation assay demonstrated that the surviving fraction of U87 cells treated by TMZ in combination with alpha irradiation was lower than was achieved by alpha- or x-ray irradiation as monotherapies, or by x-ray combined with TMZ. The treatment of U87-bearing mice with DaRT and TMZ delayed tumor development more than the monotherapies. Unlike other radiation types, alpha radiation did not increase VEGF secretion from U87 cells in culture. BEV treatment introduced several days after DaRT implantation improved tumor control, compared to BEV or DaRT as monotherapies. The combination was also shown to be superior when starting BEV administration prior to DaRT implantation in large tumors relative to the seed size. BEV induced a decrease in CD31 staining under DaRT treatment, increased the diffusive spread of 224Ra progeny atoms in the tumor tissue, and decreased their clearance from the tumor through the blood. Taken together, the combinations of DaRT with standard-of-care chemotherapy or antiangiogenic therapy are promising approaches, which may improve the treatment of GBM patients.

ANXA1: An Important Independent Prognostic Factor and Molecular Target in Glioma

Objective: The expression, prognosis, and related mechanisms of ANXA1 are investigated in glioma, with the objective to find potential therapeutic molecular targets for glioma. Methods: We analyzed the gene expression of ANXA1 using glioma-related databases, including the Chinese Glioma Genome Atlas (CGGA) database, The Cancer Genome Atlas (TCGA) database, and the Gene Expression Omnibus (GEO) database. Moreover, we collected the sample tissues and corresponding paracancerous tissues of 23 glioma patients and then conducted a Western blot experiment to verify the expression and correlate survival of ANXA1. Moreover, we generated survival ROC curves, performing univariate and multivariate Cox analyses and the construction of the nomogram. Differential expression analysis was conducted by high and low grouping based on the median of the ANXA1 gene expression values. We conducted Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and Gene Set Enrichment Analysis (GSEA) to explore possible mechanisms, and gene co-expression analysis was also performed. Results: The results showed that the ANXA1 expression level was higher in gliomas than in normal tissues, and a high expression level of ANXA1 in gliomas was associated with poorer prognosis. The independent prognosis analysis showed that the ANXA1 gene was an independent prognostic factor of glioma. In the analysis of KEGG and Gene Set Enrichment Analysis (GSEA), it is shown that ANXA1 may play an important role in glioma patients by affecting extracellular matrix (ECM)-receptor interaction and the focal adhesion signal pathway. The core genes, including COL1A1, COL1A2, FN1, ITGA1, and ITGB1, were screened for gene correlation and prognosis analysis. The expression level of the five genes was verified by qPCR in glioma. We concluded that these five core genes and ANXA1 could play a synergistic role in gliomas. Conclusion: The results indicated that a high expression level of ANXA1 leads to worse prognosis and ANXA1 is an independent prognostic factor and a potentially important target for the treatment of gliomas.

Transcriptome Analysis and Single-Cell Sequencing Analysis Constructed the Ubiquitination-Related Signature in Glioma and Identified USP4 as a Novel Biomarker

Background

Glioma, the most frequent malignant tumor of the neurological system, has a poor prognosis and treatment problems. Glioma’s tumor microenvironment is also little known.

Methods

We downloaded glioma data from the TCGA database. The patients in the TCGA database were split into two groups, one for training and the other for validation. The ubiquitination genes were then evaluated in glioma using COX and Lasso regression to create a ubiquitination-related signature. We assessed the signature’s predictive usefulness and role in the immune microenvironment after it was generated. Finally, in vitro experiment were utilized to check the expression and function of the signature’s key gene, USP4.

Results

This signature can be used to categorize glioma patients. Glioma patients can be separated into high-risk and low-risk groups in both the training and validation cohorts, with the high-risk group having a significantly worse prognosis (P<0.05). Following further investigation of the immune microenvironment, it was discovered that this risk grouping could serve as a guide for glioma immunotherapy. The activity, invasion and migration capacity, and colony formation ability of U87-MG and LN229 cell lines were drastically reduced after the important gene USP4 in signature was knocked down in cell tests. Overexpression of USP4 in the A172 cell line, on the other hand, greatly improved clonogenesis, activity, invasion and migration.

Conclusions

Our research established a foundation for understanding the role of ubiquitination genes in gliomas and identified USP4 as a possible glioma biomarker.

In vitro and in vivo evaluation of 211At-labeled fibroblast activation protein inhibitor for glioma treatment

Glioma is the most common primary intracranial tumor without effective treatment. Positron emission tomography tracers labeled with 68Ga targeting fibroblast activation protein (FAP) have shown favorable characteristics in the diagnosis of glioma. However, to the best of our knowledge, FAP-targeted endoradiotherapy has never been explored in glioma. Hence, in this study, we investigated the therapeutic effect of 211At-labeled fibroblast activation protein inhibitor (FAPI) for glioma in vitro and in vivo. By astatodestannylation reaction, we prepared 211At-FAPI-04 with a radiochemical yield of 45 ± 6.7% and radiochemical purity of 98%. With good stability in vitro, 211At-FAPI-04 showed fast and specific binding to FAP-positive U87MG cells, and could significantly reduce the cell viability, arrested cell cycle at G2/M phase and suppressed cell proliferative efficacy. Biodistribution studies revealed that 6-fold higher accumulation in tumor sites was achieved by intratumoral injection in comparison with intravenous injection. In U87MG xenografts, 211At-FAPI-04 obviously suppressed the tumor growth and prolonged the median survival in a dose-dependent manner without obvious toxicity to normal organs. In addition, reduced proliferation and increased apoptosis were also observed after 211At-FAPI-04 treatment. All these results suggest that targeted alpha-particle therapy (TAT) mediated by 211At-FAPI-04 can provide an effective and promising strategy for the treatment of glioma.

ESPL1 Is a Novel Prognostic Biomarker Associated With the Malignant Features of Glioma

Research has confirmed that extra spindle pole bodies-like 1 (ESPL1), an etiological factor, promotes the malignant progression of cancers. However, the relationship between ESPL1 and glioma has not yet been demonstrated. The purpose of this study was to reveal the potential mechanisms of ESPL1-mediated malignant glioma progression. Gene expression data and detailed clinical information of glioma cases were obtained from multiple public databases. Subsequently, a series of bioinformatics analyses were used to elucidate the effects of ESPL1 on glioma. The results demonstrated that the mRNA and protein levels of ESPL1 in glioma were higher than those in normal brain tissues. In addition, ESPL1 expression was considerably associated with the clinical and pathological features of gliomas, such as World Health Organization grade, histology, and 1p19q co-deletion status. Importantly, ESPL1 reduced the overall survival (OS) of glioma patients and had prognostic value for gliomas. Gene set enrichment analysis (GSEA) indirectly revealed that ESPL1 regulates the activation of cancer-related pathways, such as the cell cycle and base excision repair pathways. In addition, we used the Connectivity Map (CMap) database to screen three molecular drugs that inhibit ESPL1: thioguanosine, antimycin A, and zidovudine. Finally, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression levels of ESPL1 in glioma cell lines. This study plays an important role in revealing the etiology of glioma by revealing the function of ESPL1, providing a potential molecular marker for the diagnosis and treatment of glioma, especially low-grade glioma.

Peptide Receptor Radionuclide Therapy and Primary Brain Tumors: An Overview

Primary brain tumors (PBTs) are some of the most difficult types of cancer to treat, and despite advancements in surgery, chemotherapy and radiotherapy, new strategies for the treatment of PBTs are needed, especially for those with poor prognosis such as inoperable/difficult-to-reach lesions or relapsing disease. In regard to the last point, malignant primary brain tumors remain some of the most lethal types of cancer. Nuclear medicine may provide exciting new weapons and significant contributions in the treatment of PBTs. In this review, we performed literature research in order to highlight the possible role of peptide receptor radionuclide therapy (PRRT) in the treatment of PBTs with radiolabeled molecules that bind with high-affinity transmembrane receptors such as somatostatin receptors (SSTRs), neurokinin type-1 receptor and prostate-specific membrane antigen (PSMA). These receptors are overexpressed in some cancer types such as gliomas, meningiomas, pituitary tumors and medulloblastomas. A comprehensive overview of possible applications in this field will be shown, providing knowledge about benefits, feasibility, developments and limitations of PRRT in this type of tumor, also revealing new advantages in the management of the disease.

Progress in Targeted Alpha-Particle-Emitting Radiopharmaceuticals as Treatments for Prostate Cancer Patients with Bone Metastases

Bone metastasis remains a major cause of death in cancer patients, and current therapies for bone metastatic disease are mainly palliative. Bone metastases arise after cancer cells have colonized the bone and co-opted the normal bone remodeling process. In addition to bone-targeted therapies (e.g., bisphosphonate and denosumab), hormone therapy, chemotherapy, external beam radiation therapy, and surgical intervention, attempts have been made to use systemic radiotherapy as a means of delivering cytocidal radiation to every bone metastatic lesion. Initially, several bone-seeking beta-minus-particle-emitting radiopharmaceuticals were incorporated into the treatment for bone metastases, but they failed to extend the overall survival in patients. However, recent clinical trials indicate that radium-223 dichloride (223RaCl2), an alpha-particle-emitting radiopharmaceutical, improves the overall survival of prostate cancer patients with bone metastases. This success has renewed interest in targeted alpha-particle therapy development for visceral and bone metastasis. This review will discuss (i) the biology of bone metastasis, especially focusing on the vicious cycle of bone metastasis, (ii) how bone remodeling has been exploited to administer systemic radiotherapies, and (iii) targeted radiotherapy development and progress in the development of targeted alpha-particle therapy for the treatment of prostate cancer bone metastasis.

Alpha Radiation as a Way to Target Heterochromatic and Gamma Radiation-Exposed Breast Cancer Cells

Compact chromatin is linked to a poor tumour prognosis and resistance to radiotherapy from photons. We investigated DNA damage induction and repair in the context of chromatin structure for densely ionising alpha radiation as well as its therapeutic potential. Chromatin opening by histone deacetylase inhibitor trichostatin A (TSA) pretreatment reduced clonogenic survival and increased γH2AX foci in MDA-MB-231 cells, indicative of increased damage induction by free radicals using gamma radiation. In contrast, TSA pretreatment tended to improve survival after alpha radiation while γH2AX foci were similar or lower; therefore, an increased DNA repair is suggested due to increased access of repair proteins. MDA-MB-231 cells exposed to fractionated gamma radiation (2 Gy × 6) expressed high levels of stem cell markers, elevated heterochromatin H3K9me3 marker, and a trend towards reduced clonogenic survival in response to alpha radiation. There was a higher level of H3K9me3 at baseline, and the ratio of DNA damage induced by alpha vs. gamma radiation was higher in the aggressive MDA-MB-231 cells compared to hormone receptor-positive MCF7 cells. We demonstrate that heterochromatin structure and stemness properties are induced by fractionated radiation exposure. Gamma radiation-exposed cells may be targeted using alpha radiation, and we provide a mechanistic basis for the involvement of chromatin in these effects.

Amentoflavone suppresses cell proliferation and induces cell death through triggering autophagy-dependent ferroptosis in human glioma

AIMS

Glioma is the most common type of malignant tumor of the nervous system, and aggressiveness and recurrence are major obstacles for treatment. This study is designed to explore the effects of amentoflavone (AF) on glioma, and to investigate the underlying mechanism of the anti-cancer activities of AF.

METHODS

Cell morphology was recorded under microscopy. Cell viability and cell death ratio were determined by CCK-8 assay and lactate dehydrogenase (LDH) release assay, respectively. Cell cycle progression was assessed by flow cytometry. The levels of iron, MDA (malondialdehyde), lipid ROS, and GSH (reduced glutathione) were assessed by ELISA kit. The cycle-related proteins, ferroptosis-related protein, autophagy-related protein, and the phosphorylation of AMPK, mTOR and p70S6K were analyzed by western blotting. The autophagic flux was observed by transfecting cells with mRFP-GFP-LC3 plasmids. The xenograft murine models were established to analyze the effects of amentoflavone in vivo. The immunohistochemistry assay was performed to analyze the expression of LC3B, Beclin1, ATG5, ATG7, and ferritin heavy chain (FTH).

RESULTS

Our results showed that AF treatment led to reduction in cell viability and cell death. In addition, AF was found to block cell cycle progression in a dose-dependent manner in vitro. Following treatment with AF, the intracellular levels of iron, MDA, and lipid OS were increased, and the levels of GSH and the mitochondrial membrane potential were reduced. In addition, our results showed that AF promoted the autophagic by regulating autophagy-relevant proteins. Our results also showed that the autophagy-induction by AF was associated with regulation of AMPK/mTOR signaling. Mechanistically, the inhibition effects of AF on glioma cell were reversed by DFO, ferreostatin-1 as well as upregulation of FTH. Meanwhile, the FTH levels were increased by compound C and knockdown of ATG7. Moreover, both autophagy inhibitor Baf A1 and knockdown of ATG7 were able to compromising AF-induce ferroptosis and cell death. In vivo, the tumor growth was suppressed by AF in a dose-dependent manner. The level of MDA in the tumor tissue was increased while the level of GSH in tumor tissue was decreased by AF in a dose-dependent manner. Furthermore, the expression of LC3B, Beclin1, ATG5, ATG7 were increased, and the expression of FTH were decreased by AF in a dose-dependent manner in vivo. Conclusion These results demonstrate that AF triggered ferroptosis in autophagy-dependent manner. Our results suggest that AF has the potential to be considered as a novel treatment agent in glioma.

Beyond the Barrier: Targeted Radionuclide Therapy in Brain Tumors and Metastases

Brain tumors are notoriously difficult to treat. The blood-brain barrier provides a sanctuary site where residual and metastatic cancer cells can evade most therapeutic modalities. The delicate nature of the brain further complicates the decision of eliminating as much tumorous tissue as possible while protecting healthy tissue. Despite recent advances in immunotherapy, radiotherapy and systemic treatments, prognosis of newly diagnosed patients remains dismal, and recurrence is still a universal problem. Several strategies are now under preclinical and clinical investigation to optimize delivery and maximize the cytotoxic potential of pharmaceuticals with regards to brain tumors. This review provides an overview of targeted radionuclide therapy approaches for the treatment of primary brain tumors and brain metastases, with an emphasis on biological targeting moieties that specifically target key biomarkers involved in cancer development.

Potential for Nuclear Medicine Therapy for Glioblastoma Treatment

Glioblastoma is the most common malignant adult brain tumor and has a very poor patient prognosis. The mean survival for highly proliferative glioblastoma is only 10 to 14 months despite an aggressive current therapeutic approach known as Stupp's protocol, which consists of debulking surgery followed by radiotherapy and chemotherapy. Despite several clinical trials using anti-angiogenic targeted therapies, glioblastoma medical care remains without major progress in the last decade. Recent progress in nuclear medicine, has been mainly driven by advances in biotechnologies such as radioimmunotherapy, radiopeptide therapy, and radionanoparticles, and these bring a new promising arsenal for glioblastoma therapy. For therapeutic purposes, nuclear medicine practitioners classically use β^- particle emitters like ¹³¹I, ⁹⁰Y, ^186/188Re, or ¹⁷⁷Lu. In the glioblastoma field, these radioisotopes are coupled with nanoparticles, monoclonal antibodies, or peptides. These radiopharmaceutical compounds have resulted in a stabilization and/or improvement of the neurological status with only transient side effects. In nuclear medicine, the glioblastoma-localized and targeted internal radiotherapy proof-of-concept stage has been successfully demonstrated using β^- emitting isotopes. Similarly, α particle emitters like ²¹³Bi, ²¹¹At, or ²²⁵Ac appear to be an innovative and interesting alternative. Indeed, α particles deliver a high proportion of their energy inside or at close proximity to the targeted cells (within a few micrometers from the emission point versus several millimeters for β^- particles). This physical property is based on particle-matter interaction differences and results in α particles being highly efficient in killing tumor cells with minimal irradiation of healthy tissues and permits targeting of isolated tumor cells. The first clinical trials confirmed this idea and showed good therapeutic efficacy and less side effects, thus opening a new and promising era for glioblastoma medical care using α therapy. The objective of this literature review is focused on the developing field of nuclear medicine and aims to describe the various parameters such as targets, vectors, isotopes, or injection route (systemic and local) in relation to the clinical and preclinical results in glioblastoma pathology.

New Developments in Peptide Receptor Radionuclide Therapy

Peptide Receptor Radionuclide Therapy (PRRT) is an established treatment for non-operable or metastatic neuroendocrine neoplasms that express highly and frequently somatostatin receptors. More generally, PRRT is an attractive therapy option for delivering cytotoxic radiation to tumor cells through specific binding of a radiolabeled peptide to a molecular target. The development of imaging companions gave rise to the concept of radiotheranostics, important for in vivo tumor detection, characterization, staging but also, and more importantly, for individual patient selection and treatment. The success of somatostatin receptor targeting paved the way for the clinical translation of other peptide-based radiopharmaceuticals targeting, e.g. the receptors Cholecystokinin 2, Gastrin Releasing Peptide (GRPR), Neurokinin-1 and C-X-C motif chemokine 4 (CXCR4). While historically the Auger emitter 111In and the high-energy β- emitter 90Y were used, the vast majority of PRRT are currently performed with the medium-energy β- emitter 177Lu, while α emitters are increasingly studied in various clinical applications.

Simultaneous induction of dispersed and clustered DNA lesions compromises DNA damage response in human peripheral blood lymphocytes

Due to its ability to induce DNA damage in a space and time controlled manner, ionising radiation is a unique tool for studying the mechanisms of DNA repair. The biological effectiveness of ionising radiation is related to the ionisation density which is defined by the linear energy transfer (LET). Alpha particles are characterised by high LET, while X-rays by low LET values. An interesting question is how cells react when exposed to a mixed beam of high and low LET radiation. In an earlier study carried out with human peripheral blood lymphocytes (PBL) we could demonstrate that alpha radiation X-rays interact in producing more chromosomal aberrations than expected based on additivity. The aim of the present investigation was to look at the mechanism of the interaction, especially with respect to the question if it is due to an augmented level of initial damage or impaired DNA repair. PBL were exposed to various doses of alpha particles, X-rays and mixed beams. DNA damage and the kinetics of damage repair was quantified by the alkaline comet assay. The levels of phosphorylated, key DNA damage response (DDR) proteins ATM, p53 and DNA-PK were measured by Western blotting and mRNA levels of 6 damage-responsive genes were measured by qPCR. Alpha particles and X-rays interact in inducing DNA damage above the level predicted by assuming additivity and that the repair of damage occurs with a delay. The activation levels of DDR proteins and mRNA levels of the studied genes were highest in cells exposed to mixed beams. The results substantiate the idea that exposure to mixed beams presents a challenge for the cellular DDR system.

Application of Neurokinin-1 Receptor in Targeted Strategies for Glioma Treatment. Part I: Synthesis and Evaluation of Substance P Fragments Labeled with 99mTc and 177Lu as Potential Receptor Radiopharmaceuticals

Gliomas, particularly WHO grade IV glioblastoma multiforme, are one of the most common and aggressive primary tumors of the central nervous system. The neuropeptide, substance P (SP), is the physiological ligand of the neurokinin-1 (NK-1) receptor that is consistently overexpressed in glioblastoma cells. The aim of this work was to study physico-chemical and biological properties of different SP analogues labeled with technetium-99m and lutetium-177 radionuclides. The synthesized compounds were characterized in vitro by partition coefficients (logP) and their stability was investigated in various physiological solutions. Biological properties (K_d,B_max) were characterized using the U373 MG cell line. The obtained lipophilicity values of the [^99mTc]NS₃/CN-SP and [¹⁷⁷Lu]DOTA-SP radiobioconjugates were in the range of −0.3 to +0.6 and −2.5 to −5.0, respectively. The studied radiobioconjugates were stable in PBS buffer and CSF, as well as in 10 mM histidine and/or cysteine solutions whereas in human serum showed enzymatic biodegradation. [¹⁷⁷Lu]DOTA-[Thi⁸,Met(O₂)¹¹]SP(1–11), [¹⁷⁷Lu]DOTA-SP(4–11) and [¹⁷⁷Lu]DOTA-[Thi⁸,Met(O₂)¹¹]SP(5–11) radiobioconjugates bound specifically to NK-1 receptors expressed on glioblastoma cells with affinity in the nanomolar range. To conclude, the shorter analogues of SP can be used as vectors, nevertheless they still do not fulfil all requirements for preparations in nuclear medicine.

A random walk approach to estimate the confinement of α-particle emitters in nanoparticles for targeted radionuclide therapy

BACKGROUND

Targeted radionuclide therapy is a highly efficient but still underused treatment modality for various types of cancers that uses so far mainly readily available β-emitting radionuclides. By using α-particle emitters several shortcomings due to hypoxia, cell proliferation and in the selected treatment of small volumes such as micrometastasis could be overcome. To enable efficient targeting longer-lived α-particle emitters are required. These are the starting point of decay chains emitting several α-particles delivering extremely high radiation doses into small treatment volumes. However, as a consequence of the α-decay the daughter nuclides receive high recoil energies that cannot be managed by chemical radiolabelling techniques. By safe encapsulation of all α-emitters in the decay chain in properly sized nanocarriers their release may be avoided.

RESULTS

The encapsulation of small core nanoparticles loaded with the radionuclide in a shell structure that safely confines the recoiling daughter nuclides promises good tumour targeting, penetration and uptake, provided these nanostructures can be kept small enough. A model for spherical nanoparticles is proposed that allows an estimate of the fraction of recoiling α-particle emitters that may escape from the nanoparticles as a function of their size. The model treats the recoil ranges of the daughter nuclides as approximately equidistant steps with arbitrary orientation in a three-dimensional random walk model.

CONCLUSIONS

The presented model allows an estimate of the fraction of α-particles that are emitted from outside the nanoparticle when its size is reduced below the radius that guarantees complete confinement of all radioactive daughter nuclides. Smaller nanoparticle size with reduced retention of daughter radionuclides might be tolerated when the effects can be compensated by fast internalisation of the nanoparticles by the target cells.

In vitro evaluation of 225 Ac-DOTA-substance P for targeted alpha therapy of glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most malignant form of brain tumors with dismal prognosis despite treatment by surgery combined with radiotherapy and chemotherapy. The neuropeptide Substance P (SP) is the physiological ligand of the neurokinin-1 receptor, which is highly expressed in glioblastoma cells. Thus, SP represents a potential ligand for targeted alpha therapy. In this study, a protocol for the synthesis of SP labeled with the alpha emitter ²²⁵ Ac was developed and binding affinity properties were determined. The effects of ²²⁵ Ac-DOTA-SP were investigated on human glioblastoma cell lines (T98G, U87MG, U138MG) as well as GBM stem cells. A significant dose-dependent reduction in cell viability was detected up to 6 days after treatment. Also, colony-forming capacity was inhibited at the lower doses tested. In comparison, treatment with the conventional agent temozolomide showed higher cell viability and colony-forming capacity. ²²⁵ Ac-DOTA-SP treatment caused induction of late apoptosis pathways. Cells were arrested to G2/M-phase upon treatment. Increasing doses and treatment time caused additional S-phase arrest. Similar results were obtained using human glioblastoma stem cells, known to show radioresistance. Our data suggest that ²²⁵ Ac-DOTA-SP is a promising compound for treatment of GBM.

Progress in Targeted Alpha-Particle Therapy. What We Learned about Recoils Release from In Vivo Generators

This review summarizes recent progress and developments as well as the most important pitfalls in targeted alpha-particle therapy, covering single alpha-particle emitters as well as in vivo alpha-particle generators. It discusses the production of radionuclides like ²¹¹At, ²²³Ra, ²²⁵Ac/²¹³Bi, labelling and delivery employing various targeting vectors (small molecules, chelators for alpha-emitting nuclides and their biomolecular targets as well as nanocarriers), general radiopharmaceutical issues, preclinical studies, and clinical trials including the possibilities of therapy prognosis and follow-up imaging. Special attention is given to the nuclear recoil effect and its impacts on the possible use of alpha emitters for cancer treatment, proper dose estimation, and labelling chemistry. The most recent and important achievements in the development of alpha emitters carrying vectors for preclinical and clinical use are highlighted along with an outlook for future developments.

Nucleolar and spindle-associated protein 1 is a tumor grade correlated prognosis marker for glioma patients

AIMS

Despite therapeutic advances in glioma management including surgery, radiation, and chemotherapy, the improvement of patient outcome is far from satisfactory. Nucleolar and spindle-associated protein 1 (NUSAP1) is an important functional protein during mitosis, and its abnormal expression is implicated in progression of different types of tumors. However, the role of NUSAP1 in gliomas remains unclear.

METHODS

NUSAP1 expression in gliomas with different grades was investigated based on GEO glioma datasets. Kaplan-Meier survival analysis was used to evaluate its prognostic significance. In vitro assays were also performed to evaluate effects of NUSAP1 on malignant phenotypes of glioma cells by silencing NUSAP1.

RESULTS

NUSAP1 expression was correlated not only with glioma grade but also with prognosis of glioma patients. NUSAP1 depletion suppressed proliferation of U251 cells by inducing cell cycle arrest at G2/M phase and apoptosis. NUSAP1 depletion rendered U251 cells impaired migratory ability as well.

CONCLUSION

NUSAP1 is a potential prognosis marker for glioma patients and therapeutic strategies targeting NUSAP1 might hold promise in improving glioma treatment.

MicroRNA-370 suppresses the progression and proliferation of human astrocytoma and glioblastoma by negatively regulating β-catenin and causing activation of FOXO3a

Certain microRNAs (miRs) regulate the progression and metastasis of various cancer types. In the present study, the role of miR-370 in the progression and proliferation of human astrocytoma and glioblastoma cells was assessed and the underlying molecular mechanism was investigated. miR-370 levels in clinical specimens of human glioma and peritumoral tissues were determined by reverse-transcription quantitative PCR. Oligonucleotide mimics and inhibitors were transfected into the U-251MG human astrocytoma cell line and the and U-87MG glioblastoma cell line and the cell viability of was determined by an MTT assay. The expression of β-catenin and forkhead box protein (FOX)O3a was determined by western blot analysis. The results revealed that the expression of miR-370 in human glioma tissues was significantly decreased compared with that in peritumoral tissues. The miR-370 levels in patients with grade III/IV gliomas were significantly decreased compared with those in grade I/II. Transfection with miR-370 mimics inhibited the proliferation of U-251MG and U-87MG cells. Furthermore, the miR-370 levels were negatively correlated with β-catenin and positively correlated with nuclear FOXO3a. In conclusion, miR-370 inhibited the proliferation of human glioma cells by regulating the levels of β-catenin and the activation of FOXO3a, suggesting that miR-370 was a tumor suppressor in the progression of human astrocytoma and glioblastoma cells.

Gold nanoparticle bioconjugates labelled with 211At for targeted alpha therapy

Gold nanoparticles labeled with ²¹¹At are very effective in radionuclide therapy.

131I-labeled and DOX-loaded multifunctional nanoliposomes for radiotherapy and chemotherapy in brain gliomas

The codelivery of different therapeutics is a promising option because of its synergetic effects of drugs. In this study, a new combination therapy that used the doxorubicin-loaded and ¹³¹I-labeled nanoliposomes (¹³¹I-DOX-NL) was proposed to delay tumor growth of gliomas, which are characterized by significant mortality and morbidity. ¹³¹I-DOX-NL was constructed based on bovine serum albumin (BSA)-tailor made hydrophobic maleimide-functionalized poly(ε-caprolactone) (PCL) (Fig. 1) and was evaluated by cellular viability in vitro and by U87 xenograft models in vivo. Compared with using ¹³¹I-NL or DOX-NL alone, our experimental results show that ¹³¹I-DOX-NL exhibits similar high cellular uptake but enhanced efficacy to cure gliomas because of its codelivery of ¹³¹I and DOX. In the U87 mouse tumor models, the combination therapy resulted in higher survival rates of mice and smaller tumor sizes than monotherapy did alone. In conclusion, multifunctional nanoliposome ¹³¹I-DOX-NL is a good candidate for the codelivery of ¹³¹I-mediated radiotherapy and DOX-mediated chemotherapy due to its ability to inhibit U87 cell proliferation and tumor growth. ¹³¹I-DOX-NL can be used as a promising effective therapy for malignant gliomas and deserves further investigation.